In order to enhance the competitive power of future networks, the Third Generation Partnership Project (3GPP) is motivated to work on a new evolved network. The architecture of such an evolved network as illustrated in FIG. 1 includes: an evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (TRAN), abbreviated as E-UTRAN, which performs functionalities related to radio access in evolved networks; a Mobility Management Entity (MME) which is responsible for mobility management of control plane, including user context and mobility status management, user temporary identity allocation, and so on; a Serving Gateway (Serving GW) which is a user plane anchor between 3GPP access systems, terminating the interface to the E-UTRAN; a Packet Data Network Gateway (PDN GW), also referred to as Anchor Gateway, which is a user plane anchor between 3GPP and Non-3GPP access systems, terminating the interface to an external Packet Data Network (PDN); a Policy and Charging Rule Function (PCRF) which provides policy control decision and flow charging control functionalities; and a Home Subscriber Server (HSS) which stores user subscription information.
UMTS Terrestrial Radio Access Network (UTRAN) and Global System for Mobile communications (GSM)/Enhanced Data Rate for GSM Evolution (EDGE) Radio Access Network (GERAN) perform functionalities related to radio access in existing General Packet Radio Service (GPRS)/UMTS networks. Serving GPRS Supporting Node (SGSN) performs functionalities such as routing and forwarding, mobility management, session management, user information storage, etc. in the GPRS/UMTS network.
Non-3GPP IP Access Networks mainly refer to access networks defined by some Non-3GPP organizations, such as Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (Wimax), and the like.
Authentication, Authorization and Accounting Server (AAA Server) performs Authentication, Authorization and Accounting functionalities for User Equipments (UEs).
One requirement on the evolved network is to support handover between a 3GPP access system (such as GERAN/UTRAN/E-UTRAN) and a Non-3GPP access system (such as WLAN/Wimax and so on). The handover process may be implemented through an Attach procedure of a UE to a new access system. FIG. 2 is a flowchart illustrating a handover process from a Non-3GPP access system to a 3GPP access system. The handover process includes the following steps.
1. A UE may attach to a Non-3GPP access network though a Non-3GPP GW and a PDN GW.
2. The UE may initiate a handover from the Non-3GPP access system to a System Architecture Evolution (SAE) system.
3. The UE may send an Attach Request message to an MME.
4. An authentication process may be performed among the UE, the MME, and an HSS/AAA Server.
5. A Location Update and Subscriber Data Retrieval process may be performed between the MME and the HSS/AAA Server. In this process, the MME may obtain address information of the PDN GW used by the UE in the Non-3GPP access system.
6. The MME may send a Create Default Bearer Request message to a Serving GW.
7a. If the Serving GW and the PDN GW are interfaced using the GPRS Tunneling Protocol (GTP), the Serving GW may send a Create Default Bearer Request message to the PDN GW.
7b. If the Serving GW and the PDN GW are interfaced using the Proxy Mobile Internet Protocol (PMIP), the Serving GW may send a Proxy Binding Update message to the PDN GW.
8a. If the Serving GW and the PDN GW are interfaced using the GTP, the PDN GW may send back a Create Default Bearer Response message to the Serving GW.
8b. If the Serving GW and the PDN GW are interfaced using the PMIP, the PDN GW may send back a Proxy Binding Acknowledgement (ACK) message to the Serving GW.
9. The Serving GW may send back a Create Default Bearer Response message to the MME.
10. The MME may initiate a Radio Bearer Setup process to set up the radio bearer corresponding to the default bearer, and may initiate an Attach Complete process.
The following two points should be noted. (1) The handover process from the Non-3GPP system to the SAE or other 3GPP system (such as GPRS/UMTS system) may be completed through the Attach process (but not limited to the Attach process), and actually may be completed though other processes. (2) If the Serving GW and the PDN GW are implemented at a same entity, the messages between the Serving GW and the PDN GW become internal messages at the entity.
During practice, the inventor of the present invention encounters the following drawbacks in above mentioned existing handover process in the prior art.
1. During handover from the Non-3GPP system to the 3GPP system, in order to guarantee service continuity for the UE, the 3GPP system need recover the resources used by the UE in the Non-3GPP system access system, however, there is no such a mechanism in the existing handover process from the Non-3GPP system to the 3GPP system.
2. In a normal 3GPP access process, the 3GPP system only creates a default bearer for the UE. However, in an access process during handover from the Non-3GPP system to the 3GPP system, the 3GPP system need recover the resources used by the UE in the Non-3GPP system access system. Above two access processes are different, and the 3GPP system need differentiate the two different access processes, but there is no such a mechanism for differentiating the different access processes in the existing 3GPP system.
3. In an access process in the existing 3GPP system, the UE initiates the establishment of one default bearer only, in other words, the MME can only initiates a Create Default Bearer process to one PDN GW. If the UE uses multiple PDN GWs in the Non-3GPP access system, the existing mechanism cannot work.
4. In the prior art, the handover between the Non-3GPP system and the 3GPP system is a “loosely coupled” handover, in other words, the UE firstly disconnects form the source system, and then completes the handover through the access process in the destination system. In such a way of handover, the service may be interrupted for a long time and may possibly be turned down. There is no mechanism in prior art about how to optimize the handover between the Non-3GPP system and the 3GPP system so as to decrease the service interruption time for the UE.
5. When the UE accesses a Non-3GPP access system, the Non-3GPP access system may allocate resources to the UE. When abnormal switch off or offline occurs on the UE, the resources allocated to the UE by the Non-3GPP access system will not be released. When the UE newly accesses to a 3GPP access system, the resources which was allocated to the UE by the Non-3GPP access system need be released, however there is no such a mechanism for handling this in the prior art.